The present invention relates to a noise absorbing apparatus used for absorbing noise superposed on a signal transmitted through a cable and, more particularly, to an apparatus in which a closed magnetic circuit is formed to absorb noise with ferrite members so as to enclose a cable.
In an electronic equipment, e.g., a computer, that processes digital signals, when noise is superposed on a signal transmitted through a cable and enters the equipment, it causes malfunction of the equipment. For this reason, various types of noise absorbing apparatuses have recently been proposed. For example, a pair of ferrite members divided in the radial direction are arranged to sandwich a cable between them, and a closed magnetic circuit that encloses the cable is constituted with these ferrite members, thereby absorbing noise superposed on the cable. The noise is prevented from entering the equipment.
In order to improve the noise absorbing effect of a noise absorbing apparatus of this type, the apparatus is preferably fixed at a predetermined position in the longitudinal direction of the cable. More specifically, when a noise absorbing apparatus of this type is to be put into practical use, the position of the apparatus with respect to the cable where the noise absorbing effect is most conspicuous must be obtained through experiments or the like, and the noise absorbing apparatus must then be fixed at the obtained position on the cable. For this purpose, conventionally, an arrangement for fixing the noise absorbing apparatus with respect to the cable is provided.
For example, in Japanese Utility Model Laid-Open No. 63-39997, projections are formed on the inner edges of cable insertion openings respectively formed in covers that support a pair of ferrite members. When the covers are closed and the ferrite members are coupled to each other, the projections come into contact with or bite into the outer coating of the cable to fix it. With this arrangement, however, since the projections are formed fixedly, if the diameter of the cable is small, the projections do not sometimes come into contact with or bite into the outer coating of the cable. If the cable has a large diameter and the outer coating is highly rigid, the covers cannot sometimes be closed.
In order to cope with these problems, Japanese Patent Laid-Open No. 3-268397 discloses a technique in which cable press pieces having end portions projecting toward the opening portions of the covers are provided. The end portions of the cable press pieces press the outer coating of the cable to clamp the cable, thereby fixing and supporting the cable. With this technique, the end portions of the cable press pieces flex in the radial direction, so that the noise absorbing apparatus can be fixed even for cables having different diameters.
According to the technique disclosed in this reference, however, the cable press pieces have a cantilevered structure in which their proximal end portions are fixed to the covers and their end portions that are brought into contact with the cable project toward the opening portions. In addition, the directions of thickness of the cable press pieces are aligned with the same direction as the inserting direction of the cable. For this reason, when they clamp the cable and are flexed in the radial direction, the cable press pieces are elastically deformed in a direction parallel to their surfaces, i.e., in a direction perpendicular to the direction of thickness. The degree of elastic deformation of the cable press pieces is thus limited, and these cable press piece are difficult to cope with various types of cables having large diameter differences. In this case, for example, if the width of the cable press pieces is decreased in order to increase the degree of elastic deformation, the clamping force is decreased to decrease the fixing support force of the noise absorbing apparatus. As a result, it is difficult to fix and support various types of cables having different diameters with a sufficiently large clamping force.